Method of preparing lubricating grease compositions



Sept. 15, 1953 R. c, JONES ETAL 2,652,366

METHOD OF PREPARING LUBRICATING GREASE COMPOSITIONS Filed Aug. 15, 19505 Sheets-Sheet l fiocEss FozTHE EEPARATlON OF A LITHIUM HYDROXSTEARATEGKEASE Fuaurae I lnven+ors: Eoberf Cdones Eober'i' d .WaH

Patented Sept. 15, 1953 METHOD OF PREPARING LUBRICATING GREASECOMPOSITIONS Robert C. Jones, Berkeley, and Robert J. Wall, Concord,Calif., assignorsto Shell Development Company, San Francisco, Calif., a.corporation of Delaware Application August 15, 1950, Serial No. 179,594

14 Claims. 1

This invention relates to the manufacture of lubricating grease andparticularly to the manufacture of a mineral oil base grease by acontinuous process.

In the conventional preparation of a lubricating grease a gelling agent,such as a soap, which is either preformed or prepared in situ and anorganic liquid carrier, such as a mineral oil of lubricating viscosity,are heated to an elevated temperature. allowed to cool statically untila gel structure has been formed. The cooled gel is then usuallysubjected to a milling operation to homogenize it to a homogeneousgrease composition. In general, however, heretofore both the apparatusand methods employed in such processes have proven unsatisfactory,especially when applied to the manufacture of quality and superiorgreases.

Quality greases are critical compositions, the size and state ofaggregation of the gelling agent therein having a pronounced effect uponthe physical properties of the finished grease, such as dimensionalstability, resistance to bleeding, etc.

The preparation of superior greases, particularly mineral oil soap-basegreases, is contingent upon the distribution of the gelling agenttherein, e. g., a soap, such as a lithium hydroxy fatty acid soap, inthe form of fibers or elongated crystals having a fairly high length toWidth ratio. The effioiency of utilization of the gelling agent as athickening agent depends upon the degree to which the gelling agent ispresent as discrete fibers, in contrast to more or less isometriccrystals or bundles of fibers. The amount of gelling agent (yield)required to achieve a given consistency (penetration) or mechanicalstability is dependent upon this efficiency of utilization. It followsthen that an important point in a grease preparative procedure is thestep wherein the gelling agent is produced in the desired fiber(crystal) form; for example, in the manufacture of a soap-base grease,the crystallization step wherein the soap is precipitated.

It is an object of this invention to provide a method for the productionof superior greases. It is another object of the invention to provide animproved method for the continuous manufacture of grease. A morespecific object of this invention is to present a method for themanufacture of a superior alkali metal soap-base grease, such as alithium hydroxy-fatty acid soap grease. These and other objects of theinvention will become apparent from the disclosure of this invention asset forth hereinafter.

The resulting heated admixture is The foregoing objects will be betterunderstood and others will become apparent from the detailed descriptionof the invention which will be made With reference to the accompanyingdrawing, wherein:

Figure I is a. process flow diagram for the manufacture of a lithiumlZ-hydroxystearatemineral lubricating oil grease according to theinvention;

Figure II is a graphical presentation of the influence of temperature,T1, upon grease conistency for a lithium IZ-hydroxystearate-mineral oilgrease;

Figure III is a graphical presentation of the influence of recycletemperature, T2, upon grease consistency for a lithiuml2-hydroxystearatemineral oil grease;

Figure IV is a graphical presentation of the relationship between thepressure drop, AP, and the recycle ratio, R,,with respect to consistencyof a lithium IZ-hydroxystearate grease; and

Figure V is a graphical presentation of the relationship betweenconsistency (penetration) of a lithium 12-hydroxystearate grease and theamount of shearing (work) performed thereupon.

In accordance with the discovery of the present invention, it has nowbeen found. that a superior grease may be obtained by a process whichcomprises: heating a slurry of a suitable gelling agent in a liquidlubricant carrier to approximately the solution temperature; rapidlycooling, as by quenching, while working the resulting admixture to atemperature substantially below said solution temperature and coolingthe resulting admixture to packaging temperature. Stated morespecifically, it has been found that a superior grease may be obtainedby a process which comprises: rapidly heating a slurry concentrate of asuitable gelling agent, such as a metallic soap of a fatty acid, in aliquid lubricant carrier, such as a mineral oil of lubricatingviscosity, to solution temperature; rapidly cooling While working theresulting admixture to a temperature substantially below said solutiontemperature at least about 25 F. below solution temperature, as forexample, by the addition thereto of liquid lubricant carrier, such asthe amount of liquid lubricant necessary to bring the proportion ofliquid lubricant present in the finished grease to the desired amount,and cooling the resulting admixture to packaging temperature with orWithout stirring as desired.

The process of the invention and the advantages to be obtained therefromare strikingly illustrated when applied to the manufacture of a lithiumhydroxy-fatty acid soap grease, specifically a lithiuml2-hydroxystearate-mineral oil.

grease, as fully described hereinafter with reference to Figure I.

Figure I is a process flow diagram of an embodiment of the invention asapplied to the preparation of lithium 12-hydroxystearate-minerallubricating oil grease.

Referring now to Figure I, a lithium 12-hydroxystearate and mineral oilslurry-concentrate, containing about 12% by weight of said soap plusdesired additives was prepared in kettle H, such as a standard Doppkettle, equipped with a suitable agitator l2 and heated therein to someconvenient temperature, say about 285 F. The temperature of about 285 F.was selected because it could easily be reached by employing steam asthe heating medium without necessitating unduly high steam pressures.The resulting slurry at a temperatureof about 285 F. leaves the kettlevia line Ill and enters a high pressure positive displacement pump itfrom which it is discharged at a suitable rate, e. g., about one-halfpound per minute, via line i8 into a high capacity, forced-film type ofheat exchanger (Votator type) [8 which is supplied with a suitable hightemperature heating medium, such as Dowtherm. The soap-oil slurry israpidly heated within the heat exchanger to some high temperature, T1,about 380 F., and emerges from said heat exchanger via line l9 whereinit is rapidly cooled (quenched) by contact with a relatively coolrecycle dilute soap-oil stream from line 2| to some temperature, T2, inthe neighborhood of 330-340 F, about 45 F. below temerature T1.

While the soap-oil admixture is quenched within line it, work is beingperformed upon it by forcing it through a shearing device 2!], such as aplug cock. Although any number of shearing devices are suitable, a plugcock is selected because of its simplicity, flexibility, low cost, etc.Furthermore, by adjusting the size of the opening in the plug cook awide range of pressure drop, APi, across the same is possible.

A relatively large portion of the quenched, sheared soap-oil admixtureat a temperature T2 is withdrawn from line It by line 24 which leads toa high pressure positive displacement type pump 25, such as a gear pumpwhich supplies the major portion of the energy required to accomplishthe shearing within plug cock 2% and also the recycling of the soap-oilmixture via line 2i. The temperature T2 is maintained and controlled byinjection from line 26 into line 2| of oil, for example, a 750 SSU at100F. pale oil, such as is used to prepare the initial slurryconcentrate. The injection oil in line 26 is supplied thereto via line28 from a high pressure positive displacement type pump 2%; the oil isheated by passing through heat exchanger 3i] wherein the temperature ofthe injection oil emerging therefrom is maintained and/or controlled bya suitable temperature control device actuated by a selected temperatureT2 in line [9 to control the amount of heat exchange fluid entering andleaving said heat exchanger 30 via lines BI and $53, respectively.

A portion of the quenched, sheared soap-oil admixture from line H?passes into a high capacity forced-film type of heat exchanger (Votatortype) 32 which is supplied with a suitable coolant, such as water. Thecooled grease emerges from heat exchanger 32 at some reducedtemperature, for instance, in the neighborhood of 100 F., and is readyfor packaging or for any other processing which may be desired.

In order to determine and demonstrate the critical influence of thevarious temperatures, such as the solution temperature, Ti, and thequenched oil-soap temperature, T2, upon the finished grease, a number ofexperiments were performed wherein various temperatures for T1 and T2were employed. Additionally, to demonstrate the effect of varyingamounts of work (shearing) performed upon grease during quenching aswell as the influence of recycle ratio, R,.thereupon, i. e., the weightratio of the recycle stream to the product stream to cooler 32, a numberof experiments were carried out wherein these factors were varied.

Specifically, the experiments consisted of passing a concentrated slurryof gelling agent and additives (about 12% by weight of the totalcomposition) a mineral oil (750 SSU at 100 F. pale oil), said slurryhaving been obtained by saponiiying hydrogenated castor oil glycerideswith lithium hydroxide to obtain a lithium hydroxystearate soap, througha Votator type heat exchanger, thence into a recycle line wherein oil isinjected, and shearing the resulting admixture by means of a suitablyadjusted plug cock and then cooling the admixture in another Votatortype heat exchanger. Quenching is accomplished due to the temperaturedifferential which exists between the top slurry temperature Tl of thesoap-oil admixture immediately after emerging from the aforesaid firstheating Votator and the maintained recycle temperature T2 of thequenched, sheared grease. This rapid cooling (quenching) should beaccomplished as quickly as possible, for example, in less than oneminute, preferably less than 30 seconds.

Steady-state conditions were deemed in effect when temperatures andpressure drops throughout the system were constant. By weighing theamount of oil injected and total grease output for a given length oftime, usually aboutlO minutes, feed rates could be established forcalculating soap content, usually about 6 by weight, of the finishedproduct. All products were homogenized and complete ASTM penetrationvalues according to AS'IM B21148, were obtained on the unhomogenized aswell ason the homogenized grease. Free alkalinities were kept under0.15% by weight expressed as weight per cent N aOI-I.

Throughout the process the physical and chemical properties of the oil,soap, the various other ingredients and additives employed and theconcentrate stream entering the continuous recycle system Weremaintained and considered constant. It was considered unlikely that anysubstantial or important difference in the structure and properties ofthe soap-oil slurry concentrate would result if the saponification timein the kettle (wherein sapom'fication of the gylcerides to produce alithium IZ-hydroxystearate soap was carried out) were varied. However,in order to eliminate this possibility the rate oi heating or thematerial therein was held constant. In addition, by holding thefeed-stream rates of the slurryeconcentrate to the heating- Votatorconstant, the effect of varying residence time in the heating-Votatorwas thereby eliminated.

The'following process variables and their ef-' feet upon the finishedgrease were considered and determined:

(1) Temperature, T1, to which the slurry-concentrate was heated in theheating-Votator. Temperature, T2, of the quenched-sheared soap-oiladmixture after passing through plug cock.

Pressure drop AP across the recycle pump which is the sum of thepressure drop, AP1, across the plug valve plus the pressure drop, .APz,in the recycle line, excluding the plug valve.

Recycle ratio, 1. e., weight ratio of soap-oil admixture passing throughrecycle pump to Weight of grease taken ofi as product per unit of time.

Effect of concentrate temperature, T1

The temperature T1 to which the concentrate was heated in theheating-Votator was varied between 360" and 420 F. while the recyclestream temperature T2 was maintained at 325 F. and the pressure drop APacross the recycle pump, and the recycle ratio, B, were maintained at 50p. s. i. and 19.5, respectively. A number of runs were made under theabove conditions and the consistencies (penetration) of the resultinggreases were determined. The results of these tests are graphicallypresented in Figure 11.

Figure II is a graphical presentation of the influence of final soap-oiltemperature, T1, (before quenching and shearing) upon consistency of alithium 12-hydroxystearate mineral oil unhomogenized grease as evidencedby penetration values of the finished grease. As can be seen from Figure11, the temperature T1 for maximum yield (a high yield is represented bya grease having a low penetration for a given amount of gelling agenttherein) is about 380 F. whereas yield rapidly decreases as thetemperature T1 is increased or decreased beyond this value.

The physical significance of this temperature (380 F.) can be readilyunderstood from the re sults of a differential thermal analysis of thesubject lithium hydroxystearate grease. Ther mal analysis studiesindicate the presence of two transition temperatures; the lowertemperature. about 330 F., can be considered as the frozen temperatureand the higher temperature, about 385 F., can be considered as thesolution temperature. Within this transition range heating causesloosening of the soap structure and increasing solubility. Substantiallycomplete solution occurs at the solution temperature.

By solution temperature is meant that temperature, as indicated bydifferential thermal analysis of the particular gelling agent-liquidlubricant system, at which the temperature differential of the two cellswithin the calorimeter has reached its greatest value. Solutiontemperature may be characterized as that temperature at whichsubstantially complete solution of the gelling agent in the liquidlubricant takes place, i. e., that temperature at which a substantialamount of the gelling agent therein is present as molecular aggregates(crystal nuclei) or at most discrete molecules approximating colloidaldimensions in size. Solution temperature may be further characterized asthat temperature at which the Tyndall beam disappears in the mixture.This is a convenient and accepted criterion of solution in colloidsystems.

As indicated hereinbefore, the state of aggregation materially affectsthe physical properties of the grease, thus any difference in thedispersion of the soap fibers contained therein will correspondinglyaffect the yield. Accordingly, as T1 approaches 380 F. the soap fiberbundles are more easily disrupted and dismembered for a given amount ofshearing, a higher degree of dispersion with accompanying increase inyield results.

persed by working.

When T is greater than 380 F., especially greater than 385 F. (thesolution temperature), the molecular aggregates (crystal nuclei) aredestroyed, decreasing the number of crystallization sites and therebycausing an increase in the particle size of the soap fibers uponcooling. Since large coarse fibers are not conducive to high yields,therefore, as a general rule, increasing T1 above the solutiontemperature for its system results in a decreasing yield. This effect,however, may be minimized by increasing the shearing stress or workperformed upon the quenched grease.

However, it has been found, for example, in batch experiments, that ifT1 is increased beyond the solution temperature for its particularsystem, an excellent grease of high yield may still be obtained byaddition thereto immediately prior to quenching of a small amount ofpreformed grease or soap to supply the crystal sites needed forrecrystallization of the fine soap crystals (fibers). It is alsopossible for the recycle stream, the quenching agent in thehereinbeforedescribed continuous process, to act as a seeding agent tosupply the crystal sites.

The solution temperature of a gelling agent in liquid carrier varieswith the type of gelling agent and liquid carrier employed (usually aliquid organic compound such as mineral oil). Thus, the solutiontemperature of lithium lZ-hydroxystearate in a mineral oil variesaccording to the viscosity and/ or average molecular weight of themineral oil, solution temperature increasing with increasing viscosity.The data in Table I illustrate the effect of increasing mineral oilviscosity on the solution temperature of lithium 12-hydroxystearatetherein. The mineral oil in each case was a refined solvent extractedrafflnate fraction.

TABLE I [Solution temperature for lithiugfi l2-hydroxystearate inmineral or Solution Temperature, F.

Viscosity SSU at .1

Additionally, in order to determine the eirect of theupstream-downstream temperature gradient of the grease on passingthrough the cooling- Vo ato a ample oi g e wa wi hd a a te to a pooreryield.

Effect of recycle temperature T2 In order to determine the effect ofrecycle temperature upon the consistency (penetration) of the grease, anumber of experiments was performed wherein the temperature T2 of thequenched-sheared grease was varied between 305 and 340 F. while thetemperature T1 of the soap-oil suspension upon emergence from theheating-Votator was maintained at 380 F and the pressure drop AP acrossthe recycle pump and the grease recycle ratio R were maintained at 50 p.s. i. and 19.5, respectively. The results of these experiments arepresented graphically in Figure III.

Figure III is a graphical presentation of the influence of the recycletemperature T2 (grease temperature after being quenched and worked) uponconsistency of the grease, as evidenced by the penetration valuesobtained.

The influence of recycle temperature T2 upon the'physical properties ofthe finished grease is complicated by two variables which are dependcuton the recycle temperature, via: (a) the temperature at which the greaseis worked (sheared) and (b) the quench temperature differential (i. e.,T1 minus T2) which controls the fiber size of the soap in the finishedgrease.

From the standpoint of (b) a maximum temperature differential isdesirable, as pointed out hereinbefore, but from the standpoint of theconsideration (a) shearing at temperatures below the frozen pointrequires a considerably greater expenditure of energy to achieve a givenstate of aggregation. Thus, Figure III indicates that shearing below 330F. has a moredeleteri ous eifect on the yield than is gained from thegreater degree of superstaturation and the accompanying increased rateof cooling.

Conversely, above 340 F. the quench temperature differential diminishes,leading to greater soap fiber size and/or coarser grease. This, inaddition to the possibility of soap fiber (crystal) reaggregation uponleaving the recycle line, leads A relationship between optimum recycletemperature corresponding to maximum yield and the lower (frozen)transition temperature is thus indicated, the optimum recycletemperature, T2, being 335 F.

A suitable method of reducing the amount of aggregation after quenchingis to quench a more dilute soap-oil concentrate.

Effect of shearing (working) In order to determine the effect ofshearing -the recycle pump were varied over a rather wide range ofvalues. The above conditions were obtained by adjusting the valve coreand by the use of a variable speed drive on the recycle pump (gearpump). The results of these experiments are graphically presented inFigures IV and V.

Figure IV is a graphical presentation of the relationship between thepressure drop APi across the plug cock and the recycle ratio R withrespect to various penetration values of a lithium 12-hydroxystearategrease.

Figure V is a graphical presentation of the relationship betweenconsistency (penetration) of a lithium lz-hydroxystearate grease and theamount of shearing (work) performed thereupon. I

Referring now to Figure IV wherein are plotted lines of constantpenetration, the family of curves indicates some relationship to, thelaws of constant energy input, i. e., the product of recycle ratio andthe pressure drop across the plug valve. Expressing the above in termsof unit rate of feed gives units of power per unit rate of finishedgrease output or, if time is cancelled from the expression, in work perunit mass of finished grease (W/m).

Referring now to Figure V, the best correlation between shearing workperformed per unit mass of finished grease (W/m) and consistency(penetration) is obtained when the pressure drop employed to determinethe rate of energy expended in shearing the grease is taken as the sumof pressure drop across the plug valve (APi) plus one-tenth (031) of thevalue of the recycle line pressure drop APZ, excluding the plug valve.This relationship is shown in Figure V using the log scale for the valueof W/rn merely for convenience of illustration. As indicated by FigureV, the degree of shearing should be at least about 4000 ft. pounds perpound of finished grease, while the optimum amount of shearing is in theneighborhood of above about' i500 ft. lbs. per lb. of finished grease,preferably about 8,000 ft. lbs. of work per lb. of finished grease.

Since only a small portion of the work expended on the grease results inan increase in potential energy, the rest going to thermal energy, themethod and/or means of expending this energy may be of importance. Thus,as indicated by Figure V, the energy absorbed by line friction is onlyone-tenth (0.1) as effective in hardening the grease as the energyexpended in shearing the grease through the plug cock.

All the above experiments were performed in a continuous process inaccordance with the preferred practice of the invention. That is,forming a slurry of gelling agent and liquid lubricant carrier andcontinuously heating said slurry to solution temperature, addingadditional liquid carrier, if required, to bring the components thereofto desired proportions, and continuously shearing, recycling and coolingto produce a finished grease. It is also possible to adapt the processof the invention to the so-called batchtype operation. an amount ofgelling agent and liquid carrier therefor is heated to solutiontemperature T1 in a kettle. The resulting solution is then drawn off andenters a recycle line where it is cooled to the quenched temperature T2by the addition of liquid carrier thereto and sheared, as by passingthrough a plug cock, drawing off a portion as product and recycling theremainder. If preferred, instead of adding the remaining liquid carrierrequired to bring the soap content of the finishedgrease to the desiredvalue, a mixture containing gelling agent and liquid carrier in theproportions to be found in the finished grease may be prepared in thesolution kettle In this type of batch operation and quenchingaccomplished by means of a heat exchanger while shearing.

In the above-described modified batch-type process the effect of T1 andT2 n consistency displayed the same trends as were found in thecontinuous process. In general, the yields obtained were inferior due toholding the concentrate at solution temperature in the solution kettiefor a prolonged period, resulting in complete solution of the soap andthe destruction of the crystallization sites (molecular aggregates forcrystal nuclei). Higher yields, however, were obtained by this modifiedbatch process over the conventional batch process, 1. e., less soap wasrequired to achieve a given penetration value.

Tabulated data below show the advantages of the preferred continuousprocess of the invention over a batch process. Greases, specificallylithium lz-hydrox'ysterate mineral oil greases, ri-iamifacturedaccording to the continuous process of the invention require less soap,usually about 1% to about 2% by weight of the total grease composition,to achieve a given penetration value as compared with a similar greasemanufactured by the batch process. This results in a saving of about ofthe soap required.

Although the practice of the invention and discussion of the variousoperational factors involved have been illustrated with mineral oil basegreases containing lithium IZ-hydroxystearate as the gelling agent(soap), the invention is applicable to other combinations of soaps, ormixtures" thereof, and oils. The invention, exemplified by itsapplication to a lithium hydroxystearate-mineral oi-l grease, was notintendedto be limited thereby but has been fully described therewith asillustrative of the advantages to be achieved.

The gelling agents used to form the grease may be soaps of fatty acidsand/or their glycerides. The saponifiable material may be higher fattyacids having from 10 to 32 carbon atoms and they may be saturated,unsaturated or polarsubstituted fatty acids, such as capric, lauric,myristic, palmitic, stearic, arachidic, behenic, lignoceric,myristoleic, palmitoleic, olei'c, linoleic,

ricinoleic, erucic acids, cottonseed oil fatty acids,

palm oil fatty acids, hydrogenated fish oil fatty acids, and theirmixtures and/or their glycerides, such as lard, beef, rapeseed, palm,menhaden, herring oils, etc. Other acids may be included, among whichare: acids produced by oxidation of petroleum oil and waxes, rosinacids, tall oil acids, abietic acids, including dehydroabietic acid anddihydroabietic acid; naphthenic acids, petroleum sulfonic acids and thelike.

A particularly preferred class of saponifiable materials is the class ofhydroxy fatty acids and their glycerides, such as dimethylhydroxycaprylic acids, dimethyl hydroxy caprics, hydroxy physetoleic acid,ricinoleic acid, ricinelaidic acid, 12-hydroxystearic acid,9,10-dihydroxystearic acid, l-hydroxypalmitic acid, linusic acid,sativic acid, lanoceric acid, dihydroxygadoleic, dihydroxybehenic acid,quince-oil acid and the like. The preferred hydroxy fatty acids arethose in which the hydroxy group is at least 12 carbon fit 10 atomsremoved from the carboxyl group. Also, it is preferable to use hydroxyfatty acids having at least 10 carbon atoms and up to about 32 carbonatoms and preferably those having between 14 and 32 carbon atoms in themolecule. Instead of using the free fatty acids containing a hydroxyradical their glycerides can be used such as castor oil or hydrogenatedcastor oil or mixtures of free hydroxy fatty acids and their glyceridescan be used. Mixtures of hydroxy and nonhydroxy fatty acids can be usedto form soaps for uses in the invention.

The saponifying agent used to make the soap may be metal compounds ofLi, Na, K, Cs, Ca, Sr, Ba, Cd, ZnZ, Pb and Co, and preferably theoxides, hydroxides and carbonates of the alkaline metals of valencesfrom 1 to 3. Mixtures of soaps can be used and the soaps can be made insitu or pre-made soaps can be used to form the grease. Specific examplesof preferred soaps and mixtures thereof are the alkali metal fatty acidsoaps, such as lithium stearate, lithium hydroxystearate, lithiumricinoleate, lithium soap of hydrogenated fish-oil fatty acids, lithiumsoap of mixed stearic and hydroxystearic acid, sodium stearate, sodiumhydroxystearate, sodium oleate, potassium oleate, potassium rosinate,calcium stearate, calcium hydroxystearate, barium hydroxystearate,barium stearate, barium soap of mixed stearic and hydroxystearic acids,lithium soap of mixed oleic and hydroxystearic acids, sodium soap ofmixed stearic and hydroxystearic acid; barium soap of mixed stearic andoleic acid, lead ricinoleate; mixed soaps of lithium stearate and sodiumstearate; mixed soaps of lithium hydroxystearate and sodium stearate;mixed soaps of lithium hydroxystearate and calcium stearate, etc. Aminesoaps, such as triethanolamine oleate can be used in combination withmetal soaps or as the only gelling agent.

Instead of using only soaps as the gelling agent mixtures of soaps andother gelling agents, such as organic or inorganic aerogels, e. g.,silica aerogels, alumina aerogels,. nylon or cellulose fibers can beused in addition to the soap as the gelling agent.

The soap content of grease compositions of this invention may vary overwide limits and may be as high as 50%. In practice, it is pos sible bychoice of suitable grease-forming lubricant bases to manufacturesatisfactory lubricating greases containing only about 10% or less byweight of the soap mixtures, Very satisfactory products are obtainedwith a total soap content of about 6% to 8% by weight on the finishedgrease.

The grease-forming lubricant bases used in preparing the greases of thepresent invention may vary widely in character and include mineral oilof wide viscosity range, the range: varying from about 100 SSU at 100 F.to about 2000 SSU at 100 F. The viscosity index of the oil can vary frombelow zero to about or higher and can have an average molecular Weightranging from about 250 to about 600. It may be highly refined andsolvent treated if desired by known means. A preferred mineral oil isone which has a viscosity of 300 to 700 SSU at F., a viscosity index offrom 40 to 90 or even higher and an average molecular weight of 350 to750. Instead of using straight mineral oil as the base, synthetic oilsand lubricants may be substituted in part or wholly for the mineral oil.Among the synthetic lubricants which can be used are: polymerizedolefins; polyalkylene glycols and their partial or complete ethers andesters; or-

ganic esters, e. g., 2-ethyl-hexyl sebacate, dioctyl phthalate',tri-ethylhexyl phosphate; polymeric tetrahydrofuran; polyalkyl siliconepoly mers, e. g., dimethyl silicone polymers; alkylated aromatics, suchas waxylated naphthalene, etc. Under some conditions of lubrication,minor amounts of a fixed oil such as castor oil, lard oil, etc., may beadmixed with the hydrocarbon oil and/ or synthetic oil used in makinggrease compositions of this invention.

Particularly useful stabilizing agents which can be used with greasecompositions of this inrent-ion are the alkylene glycol and/or alkylenethio glycol polymers, including their mixtures as Well as theirmonoesters and ether polymeric derivatives. The all zylene glycolpolymeric materials, also named polyoxyalkylene diols, can berepresented by the-following general structural formula:

wherein m and n are the same or different integers in agiven moleculeand a is an integer. Preferably the polymeric alkylene glycols asrepresented by the above general formula should be such that the productof the factor a and number of carbon atoms within the brackets should beat least 6 and more.

The higher polyalkylene glycols having be tween 2 and 6 carbon atoms inthe alkylene group are most effective as additives of this inventionthose containing the ethylene propylene groups are preferred. Theaverage molecular weight of the polyalkylene glycols may be from about200 to about 7,000 and the preferred molecular weight being from about600 to 6,090, it being understood that such compositions are alwaysmixtures of various molecular species of different molecular weight.

To greases of this invention there may be added small amounts of othersoaps or salts, generally in amounts of less than 2% for additionalbenefits. For example, there may be incorporated into sodium soap greaseas described above minor amount of aluminum soap or alkali alkalineearth metal naphthenates, acetates, hydroxybenzoate,alpha-hydroxystearate, alpha-hydroxypropionate, beta-hydroxypropionate,gamma-hydroxyvalerate, Ca salt of an allylphenolformaldehydecondensation product, Zn dibutyldithiocarbamate, etc.

Minor amounts of oxidation inhibitors can be added to greasecompositions of this invention with benefit such N-butyl paraphenylenediamine. Also effective as oxidation inhibitors are alpha or betanaphthylamine, phenyl-alpha or beta, naphthylamine, alpha-alpha,beta-beta dinaphthylamine, diphenylamine,tetramethyl-diamino-diphenylmethane, petroleum alkyl phenols, and2,4-ditertiary-butyl-6-methyl phenol.

Corrosion inhibitors which are particularly applicable with compositionsof this invention are bl-primary amines containing at least 6 up to 18and more carbon atoms in the molecule such as hexylamine, octylamine,decylamine, dodecylamine, octadecylamine, heterocyclicnitrogencontaining organic compounds such as alkyl substitutedoxazolines and oxazoline salts of fatty acids.

Extreme pressure agents can be added to such grease and the preferredagents comprise esters of phosphorus acids such as triaryl-,alkylhydroxy-, allryl-, aralkyh, phosphates, thiophosphates, orphosphites, etc., neutral aromatic sul fur compounds such as diarylsulfides and polysulfides, e. g., diphenyl sulfide, dicresol sulfide,dibenzyl sulfide, methyl butyl diphenol sulfide, etc., diphenyl selenideand diselenide, dicresol selenide and polyselenide, etc., sulfurizedfatty oils or esters of fatty acids and monohydric alcohols, e. g.,sperm oil, jojoba oil, etc., in which the sulfur is tightly bound;sulfurized long-chainolefins obtained by dehydrogenation or cracking ofwax; sulfurized phosphorized fatty oils, acids, esters and ketones,phosphorus acid esters having sulfurized organic radicals, such asesters of phosphoric or phosphorus acids with hydroxy fatty acids,chlorinated hydrocarbons such as chlorinated paraffins, aromatichydrocarbons, terpenes, mineral lubricating oils, etc., or chlorinatedesters of fatty acids containing the chlorine in positions other thanthe alpha position.

Additional ingredients which can be added are anti-wear agents such asoil-soluble urea or thiourea derivatives, e. g., urethanes,alliophanates, carbazides, carbazones, etc.; or rubber, polyisobutylene,polyvinyl esters, etc.; viscosity index (V. I.) improvers such aspolyisobutylene having a molecular weight above about 800, voltolizedparaffin wax, unsaturated polymerized esters of fatty acids andmonohydric alcohols, etc.; oiliness agents such as stearic and oleicacids and pour point depressors such as chlorinated naphthalene tofurther lower the pour point of the lubricant.

The amount of the additives can be added to grease compositions of thisinvention in around about 0.01% up to less than 10% by weight andpreferably from 0.1 to 5.0% by weight.

Greases manufactured according to this invention are applicable forgeneral automotive uses, and are excellent aircraft greases, industrialgreases and the like.

We claim as our invention:

1. A process for the preparation of a lubricating grease which comprisesheating a mixture of a lubricating oil and a grease-forming amount of agelling agent therefor to about solution temperature T1, quenching theheated mixture in a period of time less than about one minute to a lowertemperature T2 between about 25 F. and 55 F. lower than said solutiontemperature T1 substantially all of the quenching being conducted beforeany substantial shearing of the mixture, and thereafter shearing saidmixture at temperature T2, to form a grease, the amount of shearingperformed upon said grease being at least 4,000 ft. lbs. per pound offinished grease.

2. The process of manufacturing a superior lubricating grease accordingto claim 1 wherein the liquid carrier lubricant is a mineral oil oflubricating viscosity.

3. The process of manufacturing a superior lubricating grease accordingto claim 1 wherein the gelling agent is a metal soap of a higher fattyacid.

4. The process of manufacturing a superior lubricating grease accordingto claim 1 wherein the gelling agent is a metal soap of a fatty acid andwherein the liquid carrier lubricant is a mineral oil of lubricatingviscosity.

5. The process of manufacturing a superior .lubricating grease accordingto claim 1 wherein the gelling agent is a lithium fatty acid soap.

6. The process of manufacturing a superior lubricating grease accordingto claim 1 wherein the gelling agent is lithium 12-hydroxystearate.

7. The process of manufacturing a superior lubricating grease accordingto claim 1 wherein the gelling agent is a sodium fatty acid soap.

8. A continuous process for the manufacture of a superior lubricatinggrease which comprises: continuously, rapidly heating an admixture of amineral oil of lubricating viscosity and lithium 12-hydroxystearate toabout 380 F.; rapidly cooling the resulting solution to a temperature ofabout 335 F. by commingling said resulting solution with a relativelycool recycle stream substantially all of said quenching being conductedbefore any substantial shearing of the mixture and thereafter shearingthe commingled streams at about said latter temperature, the amount ofshearing performed upon said commingled streams being at least about4,000 ft. lbs. per pound mass of finished grease product; continuouslywithdrawing a portion of said commingled streams as product andcontinuously recycling and cooling the remainder of said commingledstreams to provide said c001 recycle stream.

9. A process for the preparation of a lubricating grease which comprisesheating a mixture of a mineral lubricating oil and a grease-formingamount of lithium hydroxystearate to a temperature between the minimumsolution temperature and about 5 therebelow, at least the period ofheating above about 285 F. being carried out in a forced film heatexchanger, quenching in a period of time less than about one minute to atemperature between about 45 F. and 55 F. below said solutiontemperature, substantially all of the quenching being conducted beforeany substantial shearing of the mixture, and thereafter shearing saidmixture at about said temperature, the amount of shearing performed uponthe grease so formed being at least 4,000 ft. lbs. per pound of finishedgrease.

10. A process according to claim 9, wherein the lithium hydroxystearateis lithium 12-hy droxystearate.

11. A process according to claim 9, wherein the minimum solutiontemperature is between 375 F. and 390 F.

12. A grease-forming process which comprises heating a minerallubricating oil having a viscosity of between 100 and 1500 SSU at 100 F.and a gelling amount of lithium lz-hydroxystearate to a temperaturebetween about the minimum solution temperature and about 5 F.therebelow, quenching said grease in a period of time less than aboutone minute to a temperature between about 45 F. and about 55 F. belowsaid solution temperature, substantially all of the quenching beingconducted before any substantial shearing of the mixture, by theaddition of mineral oil to said mixture, and shearing the soap and oilto a grease structure at about said latter temperature, the amount ofthereafter shearing performed upon said grease being between 4500 and8000 ft. lbs. per pound of finished grease.

13. A grease-forming process which comprises rapidly heating a mixtureof a lubricating oil and a gelling proportion of a grease-forming soapto a temperature between about the minimum solution temperature and 5 F.therebelow; quenching said mixture to a temperature between about 25 F.and about 55 F. below said solution temperature by commingling themixture with a relatively cool recycle stream and added lubricating oil,substantially all of the quenching being carried out with substantiallyno shearing, and thereafter shearing the commingled mixture at about theminimum quench temperature, the amount of shearing performed on saidcommingled mixture being at least about 4,000 ft. lbs. per pound offinished grease product, withdrawing a portion of said product andcooling and recycling it to provide said cool recycle stream.

14. A grease-forming process which comprises rapidly heating a mixtureof mineral lubricating oil having a viscosity of about 750 SSU at F. anda gelling proportion of lithium-12- hydroxy stearate to a solutiontemperature of about 380 F., quenching said mixture to about 335 F. bycommingling the mixture with a relatively cool recycle stream and addedlubricating oil, substantially all of the quenching being carried outwith substantially no shearing, and thereafter shearing the commingledmixture at about 335 F., the amount of shearing being about 8000 ft.lbs. per pound of finished grease product, withdrawing a portion of saidproduct and Cooling and recycling it to provide said cool recyclestream, the weight ratio of recycle stream to weight of finished greasebeing at least about 19.5.

ROBERT C. J ONES. ROBERT J. WALL.

References Cited in the file of this patent UNITED STATES PATENTS NumberName Date 1,943,806 Beckert et al Jan. 16, 1934 2,450,255 Puryear et al.Sept, 28, 1948 2,461,276 Hetherington Feb. 6, 1949 2,478,917 Hain Aug.16, 1949 2,480,647 Gurd et a1 Aug. 30, 1949 2,483,282 I-Ioulton Sept.27, 1949 2,497,133 Morway et al Feb. 14, 1950, 2,542,159 Stevens Feb.20, 1951 2,598,154 Bailey et al. May 27, 1952

1. A PROCESS FOR THE PREPARATION OF A LUBRICATING GREASE WHICH COMPRISESHEATING A MIXTURE OF A LUBRICATING OIL AND A GREASE-FORMING AMOUNT OF AGELLING AGENT THEREFOR TO ABOUT SOLUTION TEMPERATURE T1, QUENCHING THEHEATED MIXTURE IN A PERIOD OF TIME LESS THAN ABOUT ONE MINUTE TO A LOWERTEMPERATURE T2 BETWEEN ABOUT 25* F. AND 55* F. LOWER THAN SAID SOLUTIONTEMPERATURE T1 SUBSTANTIALLY ALL OF THE QUENCHING BEING CONDUCTED BEFOREANY SUBSTANTIAL SHEARING OF THE MIXTURE, AND THEREAFTER SHEARING SAIDMIXTURE AT TEMPERATURE T2, TO FORM A GREASE, THE AMOUNT OF SHEARINGPERFORMED UPON SAID GREASE BEING AT LEAST 4,000 FT. LBS. PER POUND OFFINISHED GREASE.